First viable sperm cells grown from scratch

FOR the first time viable mouse sperm have been grown outside the testes. If the technique can be repeated with human sperm, it could lead to new ways of treating infertile men.

Takuya Sato at Yokohama City University in Japan and colleagues extracted germ cells from the testes of newborn mice that had not yet begun producing sperm. They placed the cells in agarose gel soaked in nourishing chemicals and hormones such as fetal bovine serum and testosterone. The team had first engineered the mice so that a protein only present in fully grown sperm would fluoresce green. Sure enough, around one month later, the team spotted the glowing protein in nearly half of their samples.

Sato's team then fused the sperm with eggs from female mice and created healthy embryos. When these embryos were implanted into females they produced healthy offspring which were able to mate and give birth to their own pups.

The team also confirmed that the testes tissue could be frozen and thawed without damage (Nature, DOI: 10.1038/nature09850).

"People have been trying to do this for years, but it takes an awful lot of trial and error," says Erwin Goldberg, a cell biologist at Northwestern University in Chicago, who was not involved in the study. The key to the team's success, Goldberg says, was patience: they kept mixing chemicals in the lab until they found exactly the right recipe to keep testes cells alive in a petri dish and satisfy all their nutritional requirements.

Earlier studies using different methods achieved similar, but less promising results. In 2006, Karim Nayernia at the University of Newcastle, UK, transformed stem cells from mouse embryos into sperm cells but most of the offspring died prematurely.

If researchers could convert germ cells from an infertile man into sperm cells, they might be able to pinpoint exactly where something goes wrong in the sperm's development and fix it, says Martin Dym, a reproductive biologist at Georgetown University in Washington DC.

The technique could also help prepubescent boys with cancer, who are not yet producing mature sperm, by growing sperm cells that can be frozen before radiation therapy.

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